Branch exchange



FIG.

NOV. 3, 1942. J. DAHL 2,300,618

BRANCH EXCHANGE Filed Au 14, 1941 2 Sheets-Sheet 1 n. s. .4. o t/v4 ran:POSITION TERM/IVA TING mulwr' TERMINATING mumr lNl/ENTOR J F DAHL ATTORNEV NOV. 3, 1942. J F D BRANCH EXCHANGE Filed Aug.. 14, 1941 2Sheets-Sheet 2 new a kSuEu $.35 km m ATTORNEY Patented Nov. 3, 1942UNHTED STATS BRANCH EXCHANGE Jack F. Dalil, Millburn, N. 3., assignor toBell Telephone Laboratories, Incorporated, New York, N. Y; a corporationof New York Application August 14, 1941, Serial No. 406,792

120mm. (Cl. 179-27) This invention relates to telephone systems and hasfor its object to facilitate the handling of call overloads directed toindividual subscribers.

The telephone service of certain subscribers,

such as ball clubs, is normally handled by a brjanch exchange having asmall number of. trunks. On occasions, however, for example when theweather is uncertain, the number of incoming inquiry calls will not onlymonopolize these trunks, preventing outgoing calls, but, where thebranch exchange is connected with a crossbar central ofiice, theunsuccessful calls may employ so much of the terminating equipment thatother subscribers may also be made inaccessible.

To obviate this difiiculty, in accordance with the present invention agroup of terminating trunks appearing in jacks at a central officeoperators position, is added to the group of branch exchange trunks andthese trunks are normally made busy. When a period of traffic congestionoccurs, the operator may be informed by the office alarms or byinquiries from subscribers and will then remove the busy condition fromthe lines appearing at her position.

In order to permit calls to be originated at the branch exchange, one ormore of the regular two-way trunks are provided with means whereby theymay be made busy to terminatingv calls. This means is made dependent onthe removal of the busy condition from the extra terminating lines. tothe terminating equipment also appear in jacks at the central ofiiceoperators position topermit the operator to obtain the informationnecessary to reply to the inquiry calls and also to permit thecompletion of calls other than inquiry calls.

In the crossbar system connections to and from the subscribers linearemade over the primary and secondary line switches and the line holdmagnet of the primary switch may be operated by either the originatingor terminating control equipment. Therefore to mark a line busy-toterminatingcalls only, the circuit over which the terminating controlequipment operates the line hold magnet must be opened and groundconnected thereto while the circuit over which the originating controlequipment operates the line hold magnet must be maintained and must notbe grounded.

If the subscriber on a line so markedoriginatesa toll call, however,the'toll operator, be- Iore completing the desired connection makes aThe trunks which are marked busy number checking connection with thecalling line. In making such a connection, the marker appliesalternating current to the circuit of the line hold magnet which isnormally returned over the previous connetcion. to cause the operationof a signal at the toll operators. position. Therefore inorder to permittoll calls'to be made over the branchexchange trunks which are removedfrom terminating service, the operation of the make-busy means insertsin the hold magnet operating circuit, means, comprising a groundedautotransformer and a condenser, which is non-conducting to the directcurrent by which the hold magnet might be operated but does conduct thealternating current employed in number checking,

These features of the invention will be more apparent from aconsideration of the following description in connection with thedrawings in which:

Fig. 1 shows the operators position at the central ofiice, and

Fig. 2 shows the branch exchange and a part of the terminating controlequipment.

A crossbar telephone system of the type with which the circuits of thepresent disclosure are adapted to function i disclosed in U. S. Patent2,232,371 to J. W. Dehn et 2.1., February 18, 1941, while a systemshowing number checking applied to a slightly different crossbartelephone system may be found in U. S. Patent 2,105,921 to F. A. Korn,January 18, 1938.

At the branch exchange operators position appear jacks 2&0, 201 and 202in which terminate two-way trunks connecting the branch exchange withthe equipment at the central oilice. The trunk circuits 203, 29c and 205represent the equipment at the branch exchange individualto each trunkand since they do not enter into the present invention they have beenmerely indicated. As many such trunk circuits are provided as desirablefor normal service.

The auxiliary line circuits 2% and 281 are in-- serted at the centralofiice in the trunks terminating in jacks 260 and 2G! in order to giveaccess from the DSA operator to the branch exchange. Only a limitednumber of the branch exchange trunks would be so modified.

At the DEA operators position appear jacks. I00, Hll, Hi2 to which areconnected termina ing trunks 33, HM and H35. Asmany of these terminatingtrunks and jacks are provided. as seems desirable, perhaps two or threetimes the number of two-way trunks normally serving the branch exchange.

Jacks I and I01 connect with the auxiliary line circuits 206 and 201.The cord circuit I08 has been shown schematically only and may be anycord circuit standard for such a position.

Referring briefly to the control circuits, as set forth in the Dehn etal. patent above mentioned, the wanted line mirnber is registered in themarker which identifies the group of twenty numbers including the wantednumber and from that identification selects a number group connectorwhich connects the test terminals of the twenty lines corresponding tothe twenty numbers to the marker, In the marker, a relay is connected toeach of the twenty lines to test it and then a circuit is closed underthe control of the units register to operate a relay associated with thewanted line if that line is idle. In the case of a group of trunks thiscircuit may be extended to operate the relay associated with thefirstidle trunk of the group.

For example, in testing the trunks serving the branch exchange underconsideration the twenty block relay 208 is operated and connects thetest leads 209 to 2I5 of trunks constituting the trunk group to themarker. One of these leads extends over the back contacts of relays 2I3and 2I1 to the winding of relay 2 I 8 and battery. Therefore, if trunkcircuit 203 is busy, relay 2I8 is operated. After an interval a circuitis closed from ground over back contacts of relay 2I9 through the unitsregister 220 to the armature of relay 2I8. If trunk 203 is idle andrelay 2I8 is not operated the circuit extends to the winding of relay2I6 and battery. Relay 2H5 in operating disconnects the test relay andprepares the direct current operating circuit for the hold magnet.

If trunk'2fl3 is busy the circuit is extended as shown in detail in theabove-identified Dehn et al. patent to operate the relay correspondingto the first idle trunk in the group.

When a number checking connection is made relays 2I1 and 2I9 areoperated and alternating current from source 22I is connected over frontcontacts of relay 2I9, through the units register 220, condenser 222,front contact of relay 2 I1 and back contact of relay 2I6 to the testconductor of the trunk and thence to the sleeve conductor of theconnection outgoing to the toll operators position.

Conductor 209'and the test conductors asso ciated with the otherunmodified trunks extend directly to the test terminals and the holdmagnets of the corresponding trunks.

Conductors 2I2 to 2I5 and the testconductors of the other terminatingtrunks extend to armatures on relay H2. With relay H2 normal, ground isconnected over the back contacts of relay H2 to the test conductors tomark these terminating trunks busy. At times of traffic congestion, keyI09 is operated, closing an obvious circuit for relay H2. Relay H2operates to extend these conductors to trunk circuits I03, I94, I05,etc.

Conductors 2H) and 2I I are connected to armatures of relays H4 and H3,respectively. With these relays unoperated the conductors are connectedover back contacts of these relays and conductors H8 and H1 to theauxiliary line circuits 201 and 206. When key I09 has been operated tomake the terminating trunks available, keys H0 and III may be operated,closing circuits for relays II 3 and H4, respectively. With relayH3'operated, test conductor 2H is connected to the mid-point ofretardation coil I I5. One

terminal of coil H5 is connected to ground thereby marking the testconductor busy to the direct current test circuit of the marker. Theother terminal of coil H5 is connected through condenser IIS and thelower front contact of relay H3 to conductor H1 leading to auxiliaryline circuit 206. Relay H4 functions in a similar manner to insert coilH9 and condenser I20 between conductors 2I0 and H8. It will be seen thatcoils H5 and H9 act as autotransformers to transmit the alternatingcurrent used in number checking to the originating side of the circuitwhile preventing the passage of the direct current used in operating theline hold magnet.

The operation of the terminating trunk circuit will now be considered.

Assuming that trunk circuit I03 is the first idle one of the group, themarker tests the circuit over conductor 2I5, front contact of relay H2,conductor I23, inner lower back contact of relay I24, winding of relayI22 to battery. Therefore the test relay such as relay 2I8 does notoperate and when, subsequently, ground is connected to conductor 2I5,relay I22 operates, extending this ground over its lower front contactto conductor I2l, over which the line hold magnet is operated. Withthe'switches operated ground from the incoming trunk'circuit holds boththe hold magnet and relay I22 operated. Relay I22 connects coil I25across the tip and ring of jack I00 to provide cord circuit supervision.

When the incoming trunk applies ringing current to the tip and ringconductors I26 and I21, relay I28 operates in a circuit extending fromconductor 126 through the upper winding of relay I23, condenser I29,outer upper back contact of relay I24 to conductor I21. Relay I20 locksin a circuit from battery through its lower winding, inner upper contactof relay I22, outer lower back contact of relay I24 to ground at theouter lower contact of relay I28. At its inner lower contact relay I28closes a circuit for relay I30. Relay I30 in operating opens the talkingcircuit and connects resistance I33 in parallel with coil I3I andresistance I32 to prepare a tripping circuit for the ringing current.Relay I30 also closes a circuit from battery over its lower frontcontact, irmer upper back contact of relay I24 to lamp I34 and ground.

When the operator inserts the plug of a cord at her position in jackI00, to which lamp I34 is individual, battery on the sleeve of the cordextendsover the sleeve of jack I00 to the winding of relay I 24 andground. Relay I24 operates, extinguishes lamp I34, disconnects relay I22from conductor I23 andconnects direct ground thereto. At its outer upperfront contact relay I24 closes one break in the talking circuit andcompletes the tripping bridge prepared by relay I30. It disconnectsrelay I28 from conductor I 21, closes a discharge circuit for condenserI29 and opens the locking circuit for relay I28 which now releases,opening the circuit of relay I30, but relay I30 is slow to release tomaintain the tripping bridge for a sufiicient time to operate theringing cut-off relay at'the incoming trunk. When relay I30 releases,the talking circuit is closed through from the incoming trunk to theoperators cord. Coil I3I and resistance I32 remain connected across theincoming tip and ring conductors to operate the supervisory relay of theincoming trunk.

When the operator withdraws her cord, relay I24 releases, restoringtrunk I03to normal and opening the connection between conductors I20 andI2! to permit the incoming trunk circuit to restore.

.The auxiliary line circuit 203 will now be described. If the trunk hasnot been made busy to terminating calls, the test circuit from themarker extends as above described to conductor Ill and over the innerupper back contact of relay 230 to the winding of relay MI and battery.When the marker connects ground to conductor III'I relay 2 3'I operates,extending ground over-its inner upper front contact to conductor 232 tooperate the line hold magnet 243. After the switches have operated,ground from the incoming trunk serves to lock relay 23I. With relay 23!operated tip and ring conductors 233 and 234 are connected over theouter front contacts of relay 2-3'I and the outer back contacts of relay230 to conductors 235 and 236 leading to the P. B. X. trunk circuit 2G5.Relay 23I also connects battery through resistance 239 to conductor 240to mark the trunk .busy at the DSA operators position. At the end of thecall the release of the switches releases relay 23I and restores thecircuit to normal.

On a call originated at the branch exchange, a bridge is closed acrossconductors 235 and 2.36, completing a circuit from ground at the outerupper back contact of relay 23.1, outer upper back contact of relay 230,conductor 2 35, through the bridge in trunk circuit 285, conductor 236,lower back contact of relay 2'30, inner upper'back contact of relay 23Ito the winding of relay 231 and battery. Relay 23! operates, connectingresistance 238 between conductors 233 and 234 to simulate the removal ofthe receiver and to start the functioning of the originating controlcircuits. At its lower contact, relay 23'! connects relay 23Itoconductor 232 so that relay 23I operates when the connection has beenextended to the originating sender. Relay 231 looks to conductor 232 andconnects conductors 233 and 234 to conductors 225 and 236 over backcontacts of relay 239 to permit the branch exchange operator to dialinto the sender. The ground which operates and locks relay 213] extendsover the inner upper back contact of relay 230 to conductor II! to markthe trunk busy to terminatingcalls.

If the DSA operator wishes to call the branch exchange or to extend aconnection thereto, she tests the sleeves of jacks I06 and I01 in theusual manner. Assuming that she finds no busy battery on jack I66, whenshe inserts the plug of her cord in that jack, battery from the sleeveof the cord completes a circuit over the sleeve of jack I06, conductor2%, lower back contact of relay 23-I to the winding of relay 230 andground. Relay 230 in operating disconnects relay 23I from conductor Illand connects ground to that conductor to mark the trunk busy toterminating calls. Relay 23!) connects the tip and ring conductors 235and 236 from the trunk circuit 205 to conductors 2M and 242 leading tojack III! to establish the talking circuit.

The above operations take place as above described when the two-waytrunk is not marked busy to terminatingcalls. It will be apparent thateven with relay II4 operated, calls originated at the branch exchange orthe operators position proceed without interference. For terminatingcalls, the test circuit from the marker finds ground through coil I I5,while the operating circuit of relay 23I is opened by the insertion ofcondenser Isl-6. In the case of a toll call outgoing from the branchexchange, relay 2'3I is held operground. Current induced in the upperwinding flows through condenser H6, lower front contact of relay M3,conductor I I1, inner upper back con-' tact of relay 23B, inner upperfront contact of relay 23I to conductor 232 and thence over the out- I ogoing connection back to the marker as described in the previouslymentioned Korn patent.

What is claimed is: p p

1. In a telephone system, a group of trunks serving a single subscriber,'said'gr'oup of trunks lb comprising aplurality of subgroups, eachsubgroup terminating at a different ofiice and means for normallymarking one of said subgroups busy.

2. In a telephone system, a group of trunks serving a single subscriber,said group of trunks 20 comprising a subgroup of trunks appearing-atsaid subscribers branch exchange and 'a supplementary subgroup, anoperators position at the central office, said supplementary subgroup oftrunks appearing at said operators position,

ated over conductor 232. When the marker con- 7 means for normallymarking said supplementary subgroup busy and means for removing saidbusy condition to permit incoming calls to be answered by said operator.I

3. In a telephone system, a group of trunks serving a single subscriber,said group of trunks comprising a subgroup of two-way trunks appearingat said subscribers branch exchange and a supplementary subgroup ofterminating trunks appearing before an operator at the central office.

4. In a telephone system, a group of trunks serving a single subscriber,said group of trunks comprising a subgroup of two-way trunks appearingat said subscribers branch exchange and a supplementary subgroupofterminating trunk-s appearing before an operator at the central ofilce,means for normally marking said supplementary subgroup busy and meansfor removing said busy condition to permit incoming calls to be answeredby said operator.

5. In a telephone system, a group of trunks serving a single subscriber,said group of trunks comprising a subgroup of two-way trunks appearingat said subscribers branch exchange and a supplementary subgroup ofterminating trunks appearing before an operator at the central office,means for marking certain of said two way trunks busy to terminatingcalls and means to permit said operator to extend a call received overone of said supplementary trunks to one of said busy marked two-waytrunks.

6, In a telephone system, a group of trunks serving a single subscriber,said group of trunks comprising a subgroup of two-way trunks appearingat said subscribers branch exchange and a supplementary subgroup ofterminating trunks appearing before an operator at the central oilice,means for marking certain of said two-way trunks busy to terminatingcalls, operator controlled means for determining whether one of saidtwo-way trunks is in use, and means to permit said operator to extend acall received over one of said supplementary trunks to said one of saidbusy marked two-way trunks.

'7. In a telephone system, a group of trunks serving a singlesubscriber, said group of trunks comprising a subgroup of two-way trunksapway trunks busyto terminating calls, said marl:- ing meansbeing-efiectiveonly if the busy condition has been removed fromsaidsupplementary trunks, and means to permit said operator to extendacallreceived over one ofsaid supplementary trunks to oneof said busy markedtwo.- way trunks. V v

8. In a telephone system, a subscriber's that;

test terminal for'said line, a switch for extending connections to andfrom said line, a magnet for operating said switch;aterminating,marker-for controlling said switch, means to connect saidmarker with said test terminal, direct current means in saidmarker tooperate said magnet over said test terminal completing a connection tosaid line, alternating current means in said marker for number checkinga connection from said ,line, and means associated with said testterminal to render said directcurrent means ineffective withoutdisabling said alternating cur rent means.

9. In a-telephone system, a subscribers line, a test terminal for saidline, a switchfor extending connections to and from said line, a magnetfor operating saidswitch and connected with" 10. In a telephone system,a subscribers line,

a test terminal for said line, a switch for extending connections to andfrom said line, a magnet for operating said switch and connected wansaid terminal, aterminating marker for controlling said switch, means toconnect said marker with said test terminal, direct current means insaid marker to operate said magnet over said test terminal in completinga connection to said line, alternating current means in said marker fornumber checking a connection from said line, and means to open theconnection between said test terminal and said magnet and to inserttherein agrounded autotransformer.

"IL-In a telephone system, a branch exchange trunk, a test terminal forsaid trunk, a switch for extending connections to and from said trunk,amagnet for operating said switch, a terminating marker for controllingsaid switch, means to connect said marker with said test terminal,direct current means in said marker to operate said magnet over saidtest terminal in completing a connection to said trunk, alternatingcurrent means in said marker for number checking a connection from saidtrunk, and means to adapt said trunk to make outgoing calls only,comprising means to open the connection between said test terminal andsaid magnet and insert therein a grounded circuit element conductingonly alternating current.

12. In a telephone system, subscribers lines, test terminals for saidlines, switches for extending connections to and from said lines,magnets for operating said switches, a terminating marker forcontrolling said switches, means to connect said marker with any one ofsaid test terminals, direct current means in said marker to operate oneof said magnets over said test terminal in completing a connection tothe associated line, alternating current means in said marker for numberchecking a connection from said line,

and means associated with certain of said test terminals to render saiddirect current means ineiiective without disabling said alternatingcurrent means to permit the associated line to make outgoing calls only.

JACK F. DAHL.

